The present invention generally relates to a yoke-like attachment assembly adaptable for mounting on the lid portion of a nuclear reactor vessel or the like and engagable with the hook portion of a lifting mechanism, to allow for selective removal of the lid from the pressure vessel as may be required. In particular, the present invention is directed to an attachment assembly including a plurality of separate couplings arranged in parallel between the lifting hook and the reactor lid, with each coupling capable of supporting the entire weight of the reactor lid, in the unlikely event of the failure of the remaining coupling.
Because of the potential environmental hazard created by equipment failure in certain installations such as nuclear power stations and the like, it is essential for the safety of the equipment as well as the environment that back-up mechanical systems be capable of performing in the event of failure to the main mechanical systems. Such a back-up mechanical system is often referred to as a fail-safe system, wherein the back-up system is generally arranged in parallel with the main mechanical system and automatically provides the desired operation upon failure of the main system. One such mechanical assembly which usually involves at least one back-up coupling is the attachment assembly mounted on the reactor lid which is attachable with a lifting mechanism for selective removal of the lid from its respective pressure vessel. If a back-up coupling were not employed between the lid and the lifting hook, serious damage to the contents of the nuclear reactor pressure vessel may occur if the main coupling assembly between the lid and the lifting hook were to fail, causing the lid to impact against the contents of the pressure vessel. Furthermore, because of the presence of radiation, such a failure could prove potentially harmful to the surrounding environment.
As will be described in detail hereafter, the present invention solves the problem of providing an attachment assembly for lifting a nuclear reactor lid or the like from its respective pressure vessel, wherein the attachment assembly includes at least two parallel couplings extending between the lifting hook and the lid itself, to ensure removal of the lid in the event of the mechanical failure to one of the couplings.